1. Field of the Invention
The present invention relates to the field of alignment devices for scanned laser systems and has particular application in scanned laser lithography systems.
2. Description of the Related Art
A number of direct-write lithography systems for production of semiconductor wafers and the like are known in the art. In each of these systems, it is necessary to I1 position the wafer on a mechanical stage and accurately position the wafer under the write beam. Typically, registration marks are first written onto the substrate and subsequently such registration marks are utilized to determine the relative position of the wafer with respect to the alignment system. It may be worth noting that the registration marks may be applied on a global basis, on a die-by-die basis or on a field-by-field basis. In the case of registration marks being applied on a global basis, the wafer is accurately aligned and positioned with respect to the registration mark. In a global registration system, extreme stability of the system as well as flat, non-distorted wafers are required. In both die-by-die and field-by-field registration, the registration marks need to be applied in a manner and position compatible with the fabrication process.
In any event, what is important is the ability to accurately position a wafer with respect to a write beam in a direct-write lithography system. Therefore, as one objective of the present invention, an improved system for positioning of wafers in such a system is disclosed.
As a second objective of the present invention, improved alignment optics for presentation of relatively distortion-free images of a wafer is disclosed.
As a third objective of the present invention, an improved method for applying registration marks and an improved structure for said registration marks is disclosed. PG,5